DirectX Video Acceleration Video Subtypes
[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]
The following subtypes are used by decoders that are using DirectX Video Acceleration (DXVA). AI44 and IA44 are surfaces with a bits-per-pixel value of 8. There are 4 bits of I and 4 bits of A. I represents an index into a 16-entry YUV palette. A represents 4 bits of transparency information (also known as per-pixel-alpha). Therefore, AI44 and IA44 surfaces allow for 16 different colors at 16 different transparency values, or 256 different pixel representations. With AI44 the alpha is stored in the hi-nibble, in IA44 the alpha is stored in the lo-nibble. Both formats are very useful for DVD sub-picture images and Line21 and Teletext images. Microsoft prefers the AI44 version because it is slightly easier to generate text using this format.
| Subtype | Description |
|---|---|
| MEDIASUBTYPE_AI44 | For subpicture and text overlays. See previous description. |
| MEDIASUBTYPE_IA44 | For subpicture and text overlays. See previous description. |
Requirements
| Requirement | Value |
|---|---|
| Header |
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